Not a Mac person, but PS does do well with 2 video cards. Try disabling one.
Curt meant to say "does not do well" I think.
Your video cards appear to be older, and nVidia (through Apple) doesn't do the world's best job in keeping their display drivers in good shape for older cards..
With modern hardware one card can drive multiple monitors. Perhaps this is an indication that you need to update your hardware to run this new version of Photoshop, replacing the two video cards with one new one that's more powerful than the pair put together.
But before replacing hardware, try changing the Graphics Processor settings in the Photoshop - Preferences - Performance dialog (e.g., in the Advanced section try Basic mode). Remember to fully Quit Photoshop and restart it before testing such a configuration change.
Thank you guys. I've never had any of these problems until CS6, so it seems to be how it's using the graphics cards or maybe memory...or how it's using them in combination with something else going wrong.
Either way, to begin, I'll turn of the GUI in performance settings (it was previously in basic mode) and I'll see if that helps.
If not, it might be hardware or a bad install (PS or OS). In which case the heavier trouble shooting will begin.
If you disable the [ ] Use Graphics Processor setting entirely keep in mind you'll lose some GPU-specific features. They're listed here: http://helpx.adobe.com/photoshop/kb/photoshop-cs6-gpu-faq.html
Also, is your OS as up to date as you can make it? Apple delivers display driver updates with OS updates.
Thanks for that link Noel. I'm just going to disable it as a test...just to see if I can rule out other possibilities.
No, my OS is still on snow leopard. I'd had Lion installed but disliked it so much and had so many problems calibrating my NEC displays (using spectraview) that I rolled back.
I'm waiting for this next OS they're releasing this month supposedly to give an update another go...
Apple's support for multiple display cards is abysmal.
If you have to run more than one card, make sure the second one is identical to the first or you won't stand a chance.
The display bugs in Lion, the current Mac OS are abundant. You're wise in not upgrading to Lion.
I did mean to say PS does NOT work well with 2 video cards. You are a little better then most as they are the same.
Would still try to disable one and see how it works.
If turning off the GUI doesn't work I'll try to pull a card.
Oddly, I didn't have any of these problems with CS6 beta. It was relatively stable. This stuff all began to pop up with the purchased version. As far as I know I did the proper uninstall of the beta before installing the paid version. A drag though.
From what I can perceive there were GPU code changes between the two versions. Probably last minute feature completions or bug fixes. We simply can't know exactly what they did between the versions, and it's possible they did something that made it work less well on your particular hardware.